Compared to the other cellular organs in the human body, the intestinal epithelial cells are exposed to an enormous number of antigens that originate from ingested foods, yeast, bacteria and viruses. Some of these bacterial antigens pose no threat to the mucosal immune system, while others may be harmful to the host. The intestinal immune system monitors these bacterial antigens in the intestinal lumen by allowing a few molecules to permeate the epithelium, where they interact with the mucosal and systemic immune system, in order to develop regulatory T-cell function or tolerance for these antigens. However, inappropriate or excessive exposure of the intestinal immune system to these bacterial antigens may cause the breakdown of this regulatory mechanism and lead to gastrointestinal disease (1). Therefore, an understanding of the physiology of the antigen uptake is central to an appreciation of the pathogenesis of disease, including inflammatory and autoimmune reactions (2).
These and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Increased intestinal permeability is thought to be an early stage that precedes the onset of several autoimmune disorders (3-6). For this reason, there has recently been an increased interest in the role of intestinal barrier dysfunction in the pathogenesis of many pathological conditions targeting the GI tract as well as extra-intestinal organs including the nervous system (7). This dysregulation of the intestinal barrier function as the biological doorway to inflammation, autoimmunity and cancer was discussed in a review article by Fasano (7). In this review article, as well as an earlier Fasano article (4), Fasano emphasized that the primary functions of the gastrointestinal tract have traditionally been perceived to be limited to the digestion and absorption of nutrients and to electrolytes and water homeostasis. A more attentive analysis of the anatomic and functional arrangement of the gastrointestinal tract, however, suggests that another extremely important function of this organ is its ability to regulate the trafficking of macromolecules between the environment and the host through a barrier mechanism. Together with the gut-associated lymphoid tissue and the neuroendocrine network, the intestinal epithelial barrier, with its intercellular tight junctions, controls the equilibrium between tolerance and immunity to non-self antigens.
Zonulin/occludin are physiological modulators of paracellular tight junctions that are involved in the trafficking of macromolecules and therefore in the balance between immune response and tolerance (7). When the finely tuned intestinal barrier proteins are dysregulated in those individuals genetically susceptible to environmental factors, the possibility arises for both intestinal disorders such as celiac disease, Crohn's disease and ulcerative colitis, and extra-intestinal autoimmune diseases such as arthritis, lupus, thyroiditis, diabetes, and even multiple sclerosis (MS), malignancies and major depression (8-14). One of the major environmental factors that can contribute to the pathophysiology of gut and brain barrier dysfunction, and hence its involvement in intestinal and extra-intestinal autoimmunities, is bacterial lipopolysaccharides (LPS). Due to gut microbiota dysbiosis and bacterial translocation, LPS is apparently responsible for the activation of toll-like receptors on epithelial cells and activation of an inflammatory cascade which results first in gut barrier and then blood-brain barrier dysfunction (14). The role of LPS in the induction of “leaky gut” and “leaky brain” syndrome is shown in FIG. 1.
FIG. 1 emphasizes that GI tract abnormality can compromise the integrity of the gut barrier and increases the entry of undigested antigens into circulation, thus challenging the immune system. Reaction to these antigens activates immune and inflammatory cascades, resulting in the production of pro-inflammatory cytokines, an array of antibodies, and increased intestinal barrier permeability (or “leaky gut” syndrome). If intestinal barrier dysfunction is left unmanaged, the result could be neuroinflammation, neuroinvasion and neurodegeneration.
Therefore, there is a need for a non-invasive method, apparatus, and assays for the measurement of intestinal permeability to large antigenic molecules that can challenge the immune system, inducing inflammation, which may result in the opening of blood-brain barriers first, followed by neuroinflammation and neurodegeneration thereafter (15-25). These needs and others are met by the present invention.